This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Existing spray guns typically employ a process of liquid atomization which includes generating small liquid drops from a column or sheet of fluid dispensed from a fluid orifice. The process of atomization in typical two-phase flow conditions involves the potential energy of liquid flowing from a fluid nozzle at a high velocity as a fluid stream. When the fluid stream encounters a collinear air flow around the fluid column, it undergoes primary and secondary phases of atomization. The first phase is characterized as a solid stream near the fluid nozzle. During the secondary phase of flow, atomization takes place and fluid droplets are formed.
These fluid droplets may be shaped using shaping air flows into specific spray patterns which are generally conical shaped. As a result, the width and/or cross-section of the spray generally increases in a linear manner from an exit of the spray gun to a target surface being coated by the spray gun. In other words, the outer profile or periphery of the spray is generally characterized by an angle that is constant relative to a centerline of the spray gun. The spray velocity also decreases with distance away from the exit of the spray gun.
Thus, if the spray gun is positioned relatively close to the target surface, then the spray covers a relatively small coverage portion of the target surface at a relatively high velocity. Unfortunately, the small coverage portion can increase the time to complete a spray coating process and also reduce the uniformity in the spray coating. If the velocity of the spray is too high at this close distance, then the spray may not transfer efficiently to the target surface (i.e., poor transfer efficiency). For example, the high velocity may cause the spray to bounce off of the target surface, rather than adhering to it. As a result, the poor transfer efficiency creates more waste and pollution into the environment, while it also increases the cost for coating the target surface (i.e., a greater amount of fluid is needed to coat the surface).
If the spray gun is positioned further away from the target surface, then the spray covers a relatively larger coverage portion of the target surface at a relatively low velocity. Unfortunately, if the velocity is too low at this greater distance, then the spray may not transfer efficiently to the target surface (i.e., poor transfer efficiency). Again, the poor transfer efficiency creates more waste and pollution into the environment, while it also increases the cost for coating the target surface (i.e., a greater amount of fluid is needed to coat the surface).
As a result, a typical spray gun with a conical spray is positioned at a certain distance to ensure that the velocity is not too fast or too slow. Unfortunately, the distance may result in a small coverage area, which can decrease the uniformity in the spray coating and increase the requisite time to coat the target surface. In other words, an optimal velocity results in a less than optimal coverage area, and vice versa. The typical spray gun does not provide both an optimal velocity and an optimal coverage area due to the conical shape of the spray.